Discussion
Studies of sensitization rate to pollen have been insufficient because
of the lower allergenicity of pollen than that of house dust mites.
Further, only a few studies have investigated sensitization in
childhood. The present study is to investigate the change of
sensitization rates to pollen in children with allergic diseases taken
allergy test with altered pollen season for last 22 years. The present
outcomes have important implications for the use of phenology as an
indicator of meteorological changes. A shift in the timing of the common
tree pollen season is important as known pollens also may aggravate the
symptoms of respiratory allergic diseases. The outcome might be implied
to increase the sensitization rate to tree pollen and pollen allergy
from year to year for the past 22 years, and the age of sensitization
rate to common tree pollens was also extended to younger children under
10 age of year.
Allergic rhinitis and allergic conjunctivitis have been presented over
teen aged children9 but a number of pediatrician and
allergists have reported a gradual increase in the prevalence of
allergic diseases in children aged <6
years.17 The present study focused on the allergic
children with age 3~18 years old at Seoul metropolitan
area for the last 22 years.
As pollen exposure rates differ depending on annual weather,
sensitization rates were characterized according to these differences in
the present study. There may be implied 3 primary means by which weather
change could influence allergic sensitization to pollen.
First, warmer temperature due to climate change might increase seasonal
intensity of the allergenic load and the concentration of
pollen.18 Second, climate change could increase the
level of allergenic pollens and allergic symptoms associated with
exposure, including impacts on pollen amount, and pollen
season.2,3 Finally, CO2 concentration
and warmer temperature increase pollen concentration. And increased
CO2 might alter the allergenicity, or allergen
concentration of the pollen, and symptom
severity.11,12
The pollen season was expanded and the concentration of pollens and
sensitization rate to pollens were increased from year to year in the
present study. Sensitization to allergens is an important step in the
development of allergic diseases. A longer pollen season and increased
pollen amount could increase the opportunity of human exposure to pollen
as aeroallergens with consequences for increased allergic sensitization
in childhood.17,19
There have been a few epidemiological and experimental studies on the
relationship between allergic diseases and environmental and climate
changes.20,21 An epidemiological study presented
sensitization rate to tree pollens was significantly increased to 36.4%
in the 2010s from 19.0% in the 1990s and 8.8% in the 1980s in
Korea.22 The nationwide prevalence of “diagnosis of
allergic rhinitis, ever” was reported 15.5%, 20.4%, and 28.5% in
1995, 2000, and 2006, respectively in the Korean version of the
International Study of Asthma and Allergies in Childhood of Korean
children.23,24
Younger children might increase sensitization rate to pollen compared to
over 10 years old children with the altered pollen season in this study.
A study for children also reported the age for sensitization to weed
pollens gradually became younger (4 to 6 year of age, 3.5% in 1997 and
6.2% in 2009; 7 to 9 year of age, 4.2% in 1997 and 6.4% in
2009).17 Difference in exposure rates to allergens
with increasing age result in difference in sensitization rates.
Although the effects of environmental change on respiratory allergic
diseases are not completely understood, these differences in
sensitization rates may be implied different living environments such as
the playing outdoor and going to school in young children, conversely
adolescent stay the indoor due to hard study or playing videogames with
recent trend in Korea. It may be useful to manage allergic diseases by
continuous investigation and systematical observation of the regional
differences and chronological changes of living environments.
Oak, hazel, and alder were shown the sharpest slope to raise
sensitization rate among tree species and more related between
sensitization rate and pollen season except pine which is no to mild
allergenic, during this study. Oak is expected to dominate over other
species during the vegetation transition,25 so that
its distribution will be broader. By developing phenological models
based on weather conditions, one can assess future oak species
distribution and length of the pollen season. Hazel pollen is important,
resulting in asthma and allergic rhinitis in hazel pollen-allergic
individuals, in particular in early spring.26,27 Alder
pollen also is a significant cause of asthma, allergic rhinitis, and
allergic conjunctivitis, in particular in Spring and in conjunction with
birch and hazel pollen.28,29 In patients with
poly-sensitization to alder, hazel, and oak pollen who were
cross-reactive, initial symptoms occurred as early as February, with
abrupt exacerbation in March to May.
The accumulated temperature was the most influential variables to
pollination among meteorological variables in this study. Sensitization
rate to oak and birch had the highest correlation to accumulated
temperature among the subjected trees. Birch has reproductive rhythms of
high and low years for the abundance of pollen and subsequent seed and
pollination is dependent on the temperature.30
In conclusion, this study demonstrated the positive correlation between
the consequent changes of pollen seasons and the raising sensitization
rate to major tree pollens in childhood in Seoul metropolitan area for
the past 22 years and continuous increase in concentration of pollens
due to weather changes were expected. The sensitization rate increased
in younger children from year to year. This might imply that climate
change impact to alter the pollen season and consequently to increase
the sensitization rate to allergic tree pollens in children.